Tracheal Breathing

Insects, and some other invertebrates, exchange oxygen and carbon dioxide between their tissues and the air by a system of air-filled tubes called tracheae.

Tracheae open to the outside through small holes called spiracles. In the grasshopper, the first and third segments of the thorax have a spiracle on each side. Another 8 pairs of spiracles are arranged in a line on either side of the abdomen.

  • valves controlled by muscles that enables the grasshopper to open and close them;
  • hairs that filter out dust as the air enters the spiracles.

Spiracles open into large tracheal tubes. These, in turn, lead to ever-finer branches. The branches penetrate to every part of the body. At their extreme ends, called tracheoles, they may be less than 1 µm in diameter. Every cell in the insect’s body is adjacent to, or very close to, the end of a tracheole. In some of the flight muscles of Drosophila the tracheoles even penetrate their T-tubules bringing oxygen right next to the mitochondria that power the muscle.

This photomicrograph show how the walls of the tracheal tubes are stiffened with bands of chitin. Even so, there is a limit to the pressure they can withstand without collapsing. This may be one reason why insects are relatively small. The increased weight of the tissues of an animal the size of a rabbit, for example, would crush tracheal tubes filled only with air.

Ventilation of the Tracheal System

However, water vapor as well as carbon dioxide diffuses out of the animal, and this could pose a problem in dry environments. Drosophila avoids the risk by controlling the size of the opening of its spiracles to match the need of its flight muscles for oxygen. When oxygen demand is less, it partially closes its spiracles thus conserving body water. (See Fritz-Olaf Lehmann’s report in the 30 November 2001 issue of Science).

Large, active insects like grasshoppers, forcibly ventilate their tracheae. Contraction of muscles in the abdomen compresses the internal organs and forces air out of the tracheae. As the muscles relax, the abdomen springs back to its normal volume and air is drawn in. Large air sacs attached to portions of the main tracheal tubes increase the effectiveness of this bellowslike action.

The experiment illustrated (first performed by the insect physiologist Gottfried Fraenkel) shows that there is a one-way flow of air through the grasshopper. The liquid seals in the tubing move to the right as air enters the spiracles in the thorax and is discharged through the spiracles in the abdomen. The rubber diaphragm seals the thorax from the abdomen.

The one-way flow of air increases the efficiency of gas exchange as CO2-enriched air can be expelled without mingling with the incoming flow of fresh air.

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Tracheal System

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Abstract

This chapter describes tracheal system of insects. Insects have a tracheal respiratory system in which oxygen and carbon dioxide travel primarily through air-filled tubes called tracheae. Usually the tracheal system penetrates the cuticle via closeable valves called spiracles and ends near or within the tissues in tiny tubes called tracheoles. The tracheae primarily serve as pipes that transport gases between the spiracles and the tracheoles, whereas the thin-walled tracheoles are thought to be the main sites of gas exchange with the tissues. However, in many insects, the tracheae are compressible, and dilations of the tracheae form thin walled air sacs that together serve as bellows for enhancing the flow of gases through the tracheal system. In general, the size of the tracheal system increases with age in order to support the increased gas exchange needs of the larger insect. Major changes in tracheal structure, including changes in spiracle number and tracheal system organization, can occur at each molt and during the pupal period for endopterygote insects. The organization of the tracheal system varies dramatically among insects, with spiracle number ranging from 0 to 20 and with tracheal branching patterns varying widely across species, between body regions, and during the developmental stages of holometabolous insects.

Original language English (US)
Title of host publication Encyclopedia of Insects
Publisher Elsevier Inc.
Pages 1011-1015
Number of pages 5
ISBN (Print) 9780123741448
DOIs
  • https://doi.org/10.1016/B978-0-12-374144-8.00265-4
State Published — Dec 1 2009
See also:  Ticks in Arizona, Animals

ASJC Scopus subject areas

  • Agricultural and Biological Sciences(all)

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Encyclopedia of Insects. Elsevier Inc., 2009. p. 1011-1015.

Research output : Chapter in Book/Report/Conference proceeding › Chapter

N2 — This chapter describes tracheal system of insects. Insects have a tracheal respiratory system in which oxygen and carbon dioxide travel primarily through air-filled tubes called tracheae. Usually the tracheal system penetrates the cuticle via closeable valves called spiracles and ends near or within the tissues in tiny tubes called tracheoles. The tracheae primarily serve as pipes that transport gases between the spiracles and the tracheoles, whereas the thin-walled tracheoles are thought to be the main sites of gas exchange with the tissues. However, in many insects, the tracheae are compressible, and dilations of the tracheae form thin walled air sacs that together serve as bellows for enhancing the flow of gases through the tracheal system. In general, the size of the tracheal system increases with age in order to support the increased gas exchange needs of the larger insect. Major changes in tracheal structure, including changes in spiracle number and tracheal system organization, can occur at each molt and during the pupal period for endopterygote insects. The organization of the tracheal system varies dramatically among insects, with spiracle number ranging from 0 to 20 and with tracheal branching patterns varying widely across species, between body regions, and during the developmental stages of holometabolous insects.

AB — This chapter describes tracheal system of insects. Insects have a tracheal respiratory system in which oxygen and carbon dioxide travel primarily through air-filled tubes called tracheae. Usually the tracheal system penetrates the cuticle via closeable valves called spiracles and ends near or within the tissues in tiny tubes called tracheoles. The tracheae primarily serve as pipes that transport gases between the spiracles and the tracheoles, whereas the thin-walled tracheoles are thought to be the main sites of gas exchange with the tissues. However, in many insects, the tracheae are compressible, and dilations of the tracheae form thin walled air sacs that together serve as bellows for enhancing the flow of gases through the tracheal system. In general, the size of the tracheal system increases with age in order to support the increased gas exchange needs of the larger insect. Major changes in tracheal structure, including changes in spiracle number and tracheal system organization, can occur at each molt and during the pupal period for endopterygote insects. The organization of the tracheal system varies dramatically among insects, with spiracle number ranging from 0 to 20 and with tracheal branching patterns varying widely across species, between body regions, and during the developmental stages of holometabolous insects.

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360. The Insect Tracheal System

Description

This Biology Factsheet:
• Describes the role of gas exchange systems.
• Outlines the key differences between insect and vertebrate gas exchange systems.
• Describes the structure of the insect tracheal system.
• Explains how the components of the tracheal system are adapted for their function.

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What is Tracheal Respiration ?

Respiration through tracheae is called tracheal respiration. It is seen in insects centipedes, ticks, some mites and spiders. The respiratory pigments are absent in blood because the tracheal system distributes O2 or air directly to the cells.

Tracheal system- Tracheal system consists of 2 components: (1) Tracheae, (2) Spiracles.

Tracheae- Tracheae are system of highly branched chitin lined air tubes throughout the body. They develop due to invagination of body wall and hence lined internally by ectoderm. Histologically it is made up of outer cuticle, inner epithelial cells and a basement membrane.

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In thoracic region the main tracheal trunks form the tracheae and tracheoles. In the abdominal region there are 3 pair’s parallel longitudinal tracheal trunks. These are connected by transverse tracheae. Here the tracheae are divided into smaller tracheae and tracheoles. The tracheoles finallu end up in a terminal cell called tracheal end cell. In tracheal end cells, the tracheoles are lined with a layer of protein called trachein. At the terminal end of tracheolar lumen is filled with tracheolar fluid.

Spiracle- The tracheal system opens to outside through slit-like openings called stigmata or spiracles. In cockroach there are two pairs of spiracles in the thoracic region and 8 pairs located in the first abdominal segements. Each spiracle is surrounded by a ring-like sclerite called peritreme. The spiracles are provided with bristles which act as filters and prevent entry of dust and other particles. The spiracles are guarded by valves which are attached to the occlusor and dilator muscles for closing and opening of the aperture.

Mechanism for Gas Exchange in Tracheal System:

(i) At rest, the tracheoles are filled with a fluid by capillary action due to low osmotic pressure in tissue cells.

(ii) The oxygen of incurrent air dissolves in the tracheolar fluid and CO2 is released to air.

(iii) The fluid is absorbed into the tissue due to increased lactate concentration forduring flight.

(iv) The CO2 released during tissue oxidation is stored temporarily as bicarbonates. They act as chemoreceptor and signal in opening of spiracles. But major part of CO2 is released through cuticle.

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3.5. The tracheal system and gas exchange

In common with all aerobic animals, insects must obtain oxygen from their environment and eliminate carbon dioxide respired by their cells. This is gas exchange, distinguished from respiration, which strictly refers to oxygen-consuming, cellular metabolic processes. In almost all insects, gas exchange occurs by means of internal air-filled tracheae. These tubes branch and ramify through the body (Fig. 3.10). The finest branches contact all internal organs and tissues, and are especially numerous in tissues with high oxygen requirements. Air usually enters the tracheae via spiracular openings that are positioned laterally on the body, primitively with one pair per post-cephalic segment. No extant insect has more than 10 pairs (two thoracic and eight abdominal) (Fig. 3.11a), most have eight or nine, and some have one (Fig. 3.11c), two, or none (Fig. 3.11d-f ). Typically, spiracles (Fig. 3.10a) have a chamber, or atrium, with an opening-and-closing mechanism, or valve, either projecting externally or at the inner end of the atrium. In the latter type, a filter apparatus sometimes protects the outer opening. Each spiracle may be set in a sclerotized cuticular plate called a peritreme.

The tracheae are invaginations of the epidermis and thus their lining is continuous with the body cuticle. The characteristic ringed appearance of the tracheae seen in tissue sections (as in Fig. 3.7) is due to the spiral ridges or thickenings of the cuticular lining, the taenidia, which allow the tracheae to be flexible but resist compression (analogous to the function of the ringed hose of a vacuum cleaner). The cuticular linings of the tracheae are shed with the rest of the exoskeleton when the insect molts. Usually even the linings of the finest branches of the tracheal system are shed at ecdysis but linings of the fluid-filled blind endings, the tracheoles, may or may not be shed. Tracheoles are less than 1 µm in diameter and closely contact the respiring tissues (Fig. 3.10b), sometimes indenting into the cells that they supply. However, the tracheae that supply oxygen to the ovaries of many insects have very few tracheoles, the taenidia are weak or absent, and the tracheal surface is evaginated as tubular spirals projecting into the hemolymph. These aptly named aeriferous tracheae have a highly permeable surface that allows direct aeration of the surrounding hemolymph from tracheae that may exceed 50 µm in diameter.

In terrestrial and many aquatic insects the tracheae open to the exterior via the spiracles (an open tracheal system) (Fig. 3.11a-c). In contrast, in some aquatic and many endoparasitic larvae spiracles are absent (a closed tracheal system) and the tracheae divide peripherally to form a network. This covers the general body surface (allowing cutaneous gas exchange) (Fig. 3.11d) or lies within specialized filaments or lamellae (tracheal gills) (Fig. 3.11e,f ). Some aquatic insects with an open tracheal system carry gas gills with them (e.g. bubbles of air); these may be temporary or permanent (section 10.3.4).

The volume of the tracheal system ranges between 5% and 50% of the body volume depending on species and stage of development. The more active the insect, the more extensive is the tracheal system. In many insects, parts of tracheae are dilated or enlarged to increase the reservoir of air, and in some species the dilations form air sacs (Fig. 3.11b), which collapse readily because the taenidia of the cuticular lining are reduced or absent. Sometimes the tracheal volume may decrease within a developmental stage as air sacs are occluded by growing tissues. Air sacs reach their greatest development in very active flying insects, such as bees and cyclorrhaphous Diptera. They may assist flight by increasing buoyancy, but their main function is in ventilation of the tracheal system.

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Enlargements show: (a) an atriate spiracle with closing valve at inner end of atrium; (b) tracheoles running to a muscle fiber. (After Snodgrass 1935)

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Publisher Summary

This chapter describes tracheal system of insects. Insects have a tracheal respiratory system in which oxygen and carbon dioxide travel primarily through air-filled tubes called tracheae. Usually the tracheal system penetrates the cuticle via closeable valves called spiracles and ends near or within the tissues in tiny tubes called tracheoles. The tracheae primarily serve as pipes that transport gases between the spiracles and the tracheoles, whereas the thin-walled tracheoles are thought to be the main sites of gas exchange with the tissues. However, in many insects, the tracheae are compressible, and dilations of the tracheae form thin walled air sacs that together serve as bellows for enhancing the flow of gases through the tracheal system. In general, the size of the tracheal system increases with age in order to support the increased gas exchange needs of the larger insect. Major changes in tracheal structure, including changes in spiracle number and tracheal system organization, can occur at each molt and during the pupal period for endopterygote insects. The organization of the tracheal system varies dramatically among insects, with spiracle number ranging from 0 to 20 and with tracheal branching patterns varying widely across species, between body regions, and during the developmental stages of holometabolous insects.

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Abstract

The tracheal (respiratory) system is regarded as one of the key elements which enabled insects to conquer terrestrial habitats and, as a result, achieve extreme species diversity. Despite this fact, anatomical data concerning this biological system is relatively scarce, especially in an ontogenetic context. The purpose of this study is to provide novel and reliable information on the post‐embryonic development of the tracheal system of holometabolous insects using micro‐computed tomography methods. Data concerning the structure of the respiratory system acquired from different developmental stages (larvae, pupae and adults) of a single insect species (Tenebrio molitor) are co‐analysed in detail. Anatomy of the tracheal system is presented. Sample sizes used (29 individuals) enabled statistical analysis of the results obtained. The following aspects have been investigated (among others): the spiracle arrangement, the number of tracheal ramifications originating from particular spiracles, the diameter of longitudinal trunks, tracheal system volumes, tracheae diameter distribution and fractal dimension analysis. Based on the data acquired, the modularity of the tracheal system is postulated. Using anatomical and functional factors, the following respiratory module types have been distinguished: cephalo‐prothoracic, metathoracic and abdominal. These modules can be unambiguously identified in all of the studied developmental stages. A cephalo‐prothoracic module aerates organs located in the head capsule, prothorax and additionally prolegs. It is characterised by relatively thick longitudinal trunks and originates in the first thoracic spiracle pair. Thoracic modules support the flight muscles, wings, elytra, meso‐ and metalegs. The unique feature of this module is the presence of additional longitudinal connections between the neighbouring spiracles. These modules are concentrated around the second prothoracic and the first abdominal spiracle pairs. An abdominal module is characterised by relatively thin ventral longitudinal trunks. Its main role is to support systems located in the abdomen; however, its long visceral tracheae aerate organs situated medially from the flight muscles. Analysis of changes of the tracheal system volume enabled the calculation of growth scaling among body tissues and the volume of the tracheal system. The data presented show that the development of the body volume and tracheal system is not linear in holometabola due to the occurrence of the pupal stage causing a decrease in body volume in the imago and at the same time influencing high growth rates of the tracheal system during metamorphosis, exceeding that ones observed for hemimetabola.

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